Although the development of the embryonic chick limb is a paradigm for cellular differentiation and pattern formation, the molecular controls of this complex process are less well understood. This program project has assembled seven investigators who will direct their skills in embryology, protein chemistry, molecular biology, and invertebrate and human genetics to two major aspects of limb development. The first general topic is the normal control of specific matrix gene expression during the early stages of limb cartilage differentiation. Drs. Kosher and Upholt have defined the temporal expression of these major genes and propose to identify both cis and trans elements important for this expression. Dr. Tanzer will apply his biochemical and molecular experience to identify the new non- collagenous matrix proteins in cartilage. Dr. Lichtler has modified replication defective avian retroviruses as vehicles for gene transfer into cartilage cells that will be important in defining cis and trans elements within the cartilage matrix and in generating transgenic chicken. The second major emphasis of the grant is the analysis of naturally occurring mutations of limb development. These studies rely on identifying the mutant allele with linkage analysis to candidate genes. Dr. Clark will provide linkage in chickens with mutations of limb development while Dr. Tsipouras will apply his established expertise in RFLP analysis to families with heritable disorders of limb development. Once a mutant gene has been identified by linkage, Dr. Rowe will apply recently developed indirect RNase protection methods for mutation identification and localization. Supporting these investigators will be two cores, one with expertise in molecular biology and the other in identification and breeding of chickens with mutations of limb development. The investigators will be highly interactive in demonstrating mutations that can have adverse effect in both chicken and man and will have the ability to investigate how a mutation of a single gene can have diverse effects on many facets in the process of limb cartilage differentiation and pattern formation.